U.S. Pat. No. 4,625,955 (Cast), issued on Dec. 2, 1986, corresponding to German Patent Publication (DE-OS) 3,333,427 (Cast), describes a screw driving gun in which a positive, controlled axial feed advance motion is imposed on the screw driving blade during the screw driving. This positive controlled feed advance is provided by an additional gear drive connecting a drive motor to a spindle screw which axially advances the screw driving blade. The known apparatus is especially suitable for driving screws which have a screw pitch that corresponds substantially to the pitch of the spindle screw that imposes the controlled axial feed advance. However, there is room for improvement when the just mentioned two pitches, namely that of the screw and that of the spindle screw, deviate from one another.
While using known screw guns, including the above described screw gun, the operator must increase the axial pressure applied to the tool as the driving of each screw progresses. This requirement becomes tiresome, especially where many screws must be driven for hours on end, for example when securing sheet rock to studs. This type of work becomes even more tiring if overhead applications are involved, for example, when sheet rock is applied to ceilings.